This invention relates to improved lubricating oil compositions, and particularly relates to internal combustion engine lubricating oil formulations containing a minor amount of a new class of oil-soluble addition agents which improve the performance of the oil, particularly its detergency property.
Various additives have been developed for the purpose of imparting detergency and/or dispersancy properties to lubricating oils. Neutral and over-based metallo-organic compounds, such as the alkaline earth metal salts of sulfonic acids, and of hydrocarbon-P.sub.2 S.sub.5 reaction products were the first additives used for such purposes.
As performance levels increased and the recommended periods between oil drains lengthened for internal combustion engines, more efficient additives were needed. When high molecular weight polybutene polymers became commercially available in the early 1940's, a series of polybutene-phosphorus pentasulfide reaction products, e.g., alkaline earth salts, amine and alkylene oxide derivatives, were developed, in which the high molecular weight polybutene group enhanced their effectiveness. Other proposed additives were the amine salts, amides, imides and amidines of polybutenyl-substituted polycarboxylic acids and polymeric compounds having pendant or grafted-on polar groups. Also suggested, were combinations of alkaline earth metal sulfonates and Mannich condensation products of a low molecular weight alkyl (C.sub.2 -C.sub.20) substituted hydroxy aromatic compound, an amine and an aldehyde, and alkaline earth salts (phenates) of such Mannich condensation products.
Mannich condensation products derived from alkyl-substituted hydroxyaromatic compounds having low molecular weight alkyl substituents are described in U.S. Pat. Nos. 2,403,453; 2,353,491; 2,363,134; 2,459,112; 2,984,550; 3,036,003, and others. However, none of such prior products are suitable for use as detergent and/or dispersant additives for present day long drain oil interval in-service use.
Subsequent to the Mannich condensation products prepared with low molecular weight alkyl-substituted hydroxyaromatic compounds, e.g., alkyl phenols, lubricating oil additives were prepared by the Mannich condensation reaction in which a high molecular weight alkyl-substituted hydroxyaromatic compound, e.g. alkyl phenol, whose alkyl-substituent has an average molecular weight in the range of about 600-3,000, is reacted with an amine and formaldehyde. United States Patent No. 3,368,972 describes such products as dispersant-detergent addition agents for lubricating oils.